The present invention relates to a color selecting electrode for a color cathode-ray tube.
As a color selecting electrode used for a color cathode-ray tube, there is known a color selecting electrode, called an "aperture grill", shown in FIG. 9.
A color selecting electrode 1 shown in FIG. 9 includes a frame 6 composed of a pair of supporting members 2 and 3, and elasticity imparting members 4 and 5. The supporting members 2 and 3, each being L-shaped in cross-section, are disposed in parallel to each other with a specific gap put therebetween. The elasticity imparting members 4 and 5, each being substantially U-shaped in cross-section, are mounted to both the supporting members 2 and 3 at points, called "Bessel points", positioned inward from end portions of the supporting members 2 and 3. A large number of ribbon-like grid elements 7, arranged with a specific pitch, are mounted between both the supporting members 2 and 3 in such a manner as to be applied with a specific tensile strength, to thus form slit-like electron beam apertures 8 each between adjacent ones of the grid elements 7.
In such a color selecting electrode 1, to support the color selecting electrode 1 on an inner surface of a panel of a cathode-ray tube body at three or four points (four points in this example), supporting springs 10 (10a to 10d) are welded through spring holders 9 (9a to 9d) on four sides of the frame 6, that is, the supporting members 2 and 3 and the elasticity imparting members 4 and 5. Each of the supporting springs 10 (10a to 10d) has at its tip an engagement hole 11 to which a panel pin is to be fitted.
The color selecting electrode 1 is, as shown in FIG. 10, mounted to a panel 12 of a cathode-ray tube by fitting panel pins 13 (13a to 13d) provided on an inner surface of the panel 12 in the engagement holes 11 of the supporting springs 10 (10a to 10d), respectively.
Incidentally, in a color cathode-ray tube using the color selecting electrode 1 having such a configuration, the grid elements 7 generate heat due to electron beams upon operation of the color cathode-ray tube, and the heat thus generated is partially transmitted to the frame 6. As a result, the frame 6 is thermally expanded, to cause mislanding of electron beams.
To be more specific, as shown in FIG. 11, when the pair of the supporting members 2 and 3 are thermally expanded in the longitudinal direction as shown by a broken line due to a thermal effect of the frame 6, the grid elements 7 are correspondingly displaced as shown by a broken line. Accordingly, electron beam apertures 8, particularly, positioned at a peripheral portion are displaced as shown by a broken line. Thus, an electron beam 15, which is expected to reach a specific position P.sub.1 on a phosphor screen 16 through a specific electron beam aperture 8 located at a position A.sub.1 before thermal expansion, reaches a position P.sub.2 on the phosphor screen 16 through an electron beam aperture 8 displaced to a position A.sub.2 shown by a broken line 15' after thermal deformation of the supporting members 2 and 3 of the frame 6. This results in occurrence of mislanding of the electron beam 15.
To correct such a mislanding due to thermal expansion of the frame 6, a temperature drift correcting means having a bimetal structure has been provided on the color selecting electrode 1.
The temperature drift correcting means is so configured as shown in FIG. 9. To be more specific, each of the spring holders 9a and 9b respectively fixed on the supporting members 2 and 3 of the frame 6 has a bimetal structure. Further, a metal member 18 having a thermal expansion coefficient larger than each of the elasticity imparting members 4 and 5 is fixed on a back surface of each of the elasticity imparting members 4 and 5, and forms a bimetal structure in combination thereof.
Each of the spring holders 9a and 9b has the bimetal structure in which an outer metal member 19 having a larger thermal expansion coefficient is stuck on an inner metal member 20 having a small thermal expansion coefficient, and at an intermediate position an inwardly curved U-shape portion 21.
The temperature drift correcting means having such a bimetal structure is intended to displace the thermally expanded frame 6 on the phosphor screen 16 side as shown in FIG. 12 and hence to avoid occurrence of mislanding of electron beams.
To be more specific, when the frame 6 is thermally expanded from a state in which the frame 6 is subjected to no thermal effect (shown by a solid line) and thereby an arbitrary electron beam aperture 8 at a peripheral portion of the grid elements 7 is displaced from a position A.sub.1 to a position A.sub.2, the frame 6 is displaced to a state shown by a broken line so that the electron beam aperture 8 is shifted to a position A.sub.3 on a locus of an electron beam 15 passing through the above electron beam aperture 8 in a state in which the frame 6 is not deformed, to allow the electron beam 15 to reach a specific target position P.sub.1 on a phosphor screen 16.
Incidentally, in a high definition color cathode-ray tube (for example, a so-called non-consumer color cathode-ray tube such as a monitor tube for a computer) in which a pitch of each color phosphor layer on a phosphor screen is made finer, a landing margin for electron beams is extremely smaller than that of a consumer color cathode-ray tube.
In the case where the color selecting electrode 1, shown in FIG. 9, using the spring holders 9a and 9b and the elasticity imparting members 4 and 5 each having a bimetal structure is applied to such a high definition color cathode-ray tube, it is difficult to obtain an optimum correction for mislanding because a displacement of the color selecting electrode 1 by the bimetal structures is insufficient.
With respect to a displacement of the color selecting electrode 1, the displacement due to the spring holders 9a and 9d, each having the bimetal structure, fixed on the supporting members 2 and 3 is larger than the displacement due to the metal members 18 fixed on the elasticity imparting members 4 and 5. As a result, an attempt has been made to increase the displacement by making thin the thickness of each of the spring holders 9a and 9d having the bimetal structure or enlarging the U-shaped portion 21; however, an effect obtained by such an attempt is insufficient.
Also, if the thickness of each of the spring holders 9a and 9d having the bimetal structure is made thin, an impact resistance of a cathode-ray tube (that is, Braun tube) is deteriorated. Besides, if the U-shaped portion 21 is enlarged, there is a limitation in terms of its formed shape because there may occur cracks upon press-forming of the enlarged U-shaped portion 21. Accordingly, at present condition, it is difficult to obtain the optimum displacement of the color selecting electrode 1.
Further, since the color selecting electrode 1 is displaced by curving of the spring holders 9a and 9b each having the bimetal structure, a fitting position between the panel pin 13 and the supporting spring 10 is changed, so that the supporting spring 10 is caught by the panel pin 13 due to the change in fitting position and thereby it is not returned to the original state. This causes a variation in landing of electron beams.
On the other hand, there is known another related art color selecting electrode shown in FIG. 13. In a color selecting electrode 25 shown in FIG. 13, a metal member 24 different in thermal expansion coefficient from each of a pair of supporting members 2 and 3 is fixed at a central portion of a back surface of each of the supporting members 2 and 3 which back surface is opposed to a surface on which grid elements 7 are mounted, and forms a bimetal structure in combination thereof.
The color selecting electrode 25, however, has a problem. When the color selecting electrode 25 is subjected to a thermal effect, displacements at both end portions of each of the supporting members 2 and 3 having the bimetal structure are small. As a result, the color selecting electrode 25 cannot be practically used.